Unexplained allergies
Yesterday I had an allergic reaction on my body. I don't know whether the air or the food, was the cause of that. I had* never had this kind of allergic reaction before, that was the first time. Fortunately, I feel much better today.

* You use the past perfect "I had + (never) + verb..." to talk about a complete or uncompleted action in the past BEFORE another action in the past. In your case, "I had never had this kind of allergy..." happened before "yesterday", when you had the allergy. 

Good sentence.

Unexplained allergiesy

Yesterday in on my body(skin?) I discovered found signs of some allergic reaction, I don't know whether this is was(1) because the food or air pollution, since I have never had this kind of such an allergic reaction before., and for This was the very first time. Fortunately I am much better today.

(1) Consistent tense, past tense found (discovered and was, not found and is)

(2) for the reader a description of the reaction would have helped.  Skin Rash, blotching, mucous membrane...

老鬼